Mercury vapor discharge device



Oct. 6, 1959 A. J. HUMPHREY 2,907,905

MERCURY VAPOR DISCHARGE DEVICE Filed March 6, 1958 3 Sheets-Sheet 1INVENTOR.

ANDREW J. HUMPHREY Oct. 6, 1959 A. J. HUMPHREY MERCURY VAPOR DISCHARGEDEVICE 3 Sheets-Sheet 2 Filed March 6, 1958 FIG.Z

INVENTOR: ANDREW J. HUMPHREY Www; Mimi. my.

Oct. 6, 1959 A. J. HUMPHREY MERCURY VAPOR DISCHARGE DEVICE 3Sheets-Sheet 3 Filed March 6, 1958 FIG.7

INVENTOR. AN DREW J. HUM PHR EY The discharge device 11 is of metalconstruction and includes generally a cylindrical outer shell 12, ananode 13, and a grid 14. The metallic outer shell 12 is closed by endcaps 15 and 16, which in this embodiment are chosen to be made fromcarbon or graphite. Being of carbon they are unlikely to condensemercury on their surface as a wetted coating. A cathode 17 is on theinner surface of the cylindrical shell 12 and hence the end caps 15 and16 are electrically connected to this cathode 17.

The anode 13 is mounted along the axis 20 of the cylindrical shell 12and is supported by an anode shaft 21 electrically connected to aflexible cable 22 exterior of the device 11. The anode shaft 21 ismounted in a sleeve 23 connected by a glass seal 24 with another metalsleeve 25 connected to an end sleeve 27, in turn connected to the endcap 15. The end cap 15 has a cylindrical extension 26 relatively closelyspaced to the anode shaft 21.

The grid 14 is a cylindrical perforated metal or graphite structuresurrounding the anode 13 and generally parallel to the surface of theanode and coextensive with this surface. The perforated grid 14 iscarried on a grid shaft 29 disposed on the axis 20 with this shaft 29being supported by metal sleeves 30 and 31 and a glass seal 32 in amanner similar to the support of the anode shaft 21. An annularkeep-alive anode 33 concentrically surrounds the grid shaft 29 and ispositioned between the lower axial end of the grid 14 and the end cap16. The keepalive anode 33 is supported by mounts and lead-in terminals34 similar to the one shown and all insulated by glass seals similar to35 from an end sleeve 42 connected to the end cap 16. A startingelectrode 36 is movably carried by a bellows 37 and a glass seal 38 on alead 39. This starting electrode 36 typifies the usual startingelectrode which may be moved out of engagement with the cathode 17 tostrike an are which may move to the keepalive anode 33 to maintain asmall discharge within the device 11.

The cylindrical outer shell 12 has fixedly attached thereto as bybrazing, soldering, or other suitable means a liquid coolant coil 40which may be connected to an external cooling heat exchanger. Thecoolant coil 40 also may have an electrical terminal 41 for connectionto the cathode 17.

The outer cylindrical shell 12 is normally of a base metal, but may bethe metal desired to form the cathode 17. Typical metals in use to formthe active cathode surface are the so-called refractory metals which arenot destroyed by an arc discharge, such as molybdenum or tungsten. Sucha refractory metal may not be necessary in all cases however, dependentupon the use of the device 11. Nickel or iron may be satisfactory forthe base metal of the cathode 17 where long life of the tube is notessential. Examples of short life tube requirements could be for a surgecurrent tube or a switching tube where the life is but a few operations.The cathode 17 is a prepared active surface on the inner metal surfaceof the shell 12 and is a surface wetted with mercury. Molybdenum andtungsten are metals which can be wet with a mercury film when suchmetting takes place during the forming operation of the discharge device11 under action of an electric are or discharge between the cathode 17and anode 13. The entire exposed inner cylindrical surface of the shell12 may be wetted to form the cathode 17 or it may merely be of the typeof metal which will be capable of being wetted during use. Normally theactive cathode surface would consist of a thin sheet of rolledmolybdenum or tungsten metal spot welded to the base metal container 11.Another possibility is a sprayed or electroplated layer of refractorymetal.

The end caps 15 and 16 are electrically connected to the shell 12 andcathode 17; however, these are preferably formed from a material whichis not wetted, an example being the use of carbon or to use any common.

. 4 7 metal with the surface prepared so that it will not be easilywetted. If the metal be molybdenum, for example, it may be oxidizedbecause molybdenum oxide is not easily wetted. A more common metal maybe used for economy, for example, one of the ferrous metals, and in suchcase the inner surface of the end caps 15 and 16 and of the cylindricalextension 26 may be covered with a colloidal graphite emulsion toprevent wetting of these exposed surfaces. The end caps 15 and 16 mayalso be an insulator, such as ceramic. This construction establishesthat no portion of the envelope or of metal electrically connected tothe cathode and capable of emission from a condensed mercury layer hasaccess to the field of the anode except through the grid 14.

In operation, the device 11 is evacuated and sealed with a mercury vaporatmosphere established within the envelope formed by the shell 12 andend sleeves 27 and 42. During the manufacture of the device, the innersurface of the shell 12 is wetted at least in part with a film ofmercury and this mercury film is that which establishes the mercuryatmosphere within the device 11. This mercury film is maintained uponthe wetted area by the equilibrium between the vapor pressure of mercuryin the atmosphere inside the envelope and the vapor pressure from thewetted surface. This equilibrium will always be maintained despitechanges of temperatures of the parts of the device as long as thetemperature of the cathode does not get too much higher than that ofother parts. It is believed that the mercury film on the cathode is aform of amalgam or at least a surface amalgam which has exposed on thesurface not only mercury molecules but also molecules of the cathodemetal, such as molybdenum. The cathode can thus be at a somewhat highertemperature than the anode or grid and yet maintain this equilibrium ofvapor pressure in the envelope and pressure of vapor over the cathodefilm to cause a maintenance of mercury film on the cathode for propercontinued operation of the device. This would also remain true duringstorage periods or non-operating periods of the device.

Under operating conditions the starting electrode 36 may be used tostrike an arc which will be transferred to the keep-alive anode 33 andbe maintained at the lower end of the device 11. When the operatingpositive potential is applied to the anode 13, the customary dischargewill occur between the anode and cathode as controlled by the grid 14.The construction of the device 11 is such that a very short dischargepath is maintained between the anode 13 and cathode '17 without anyintervening bafiles. This is especially desirable in devices operatingon voltages under 1500. For higher voltage operation bafiling may beused, but for the normal voltages of one hundred to fifteen hundredvolts no baflies are required. The natural configuration of the device11 is such that heat within the device 11 maintains the anode 13 at ahigher temperature than that of the cathode 17, thence, there will be nomercury condensation on the anode 13 nor on the grid 14. The coolantcoils 40 connected to a heat exchanger permit extraction of heat fromthe device 11 so as to aid the natural temperature differential of.elements of the device 11 so that the anode 13 will always be maintainedwarmer. This makes certain thatthe film of mercury on the cathode '17will always be maintained to sustain the electric discharge. The lack ofrequirement for a pool of mercury anywhere within the device 11eliminates random vapor jets which could strike the anode 13 and thuscause failure or improper operation, and this permits a much closerspacing between the anode and cathode. The close spacing minimizes thevoltage drop in the are or electric discharge; hence, less wattage lossis incurred in the operation of the device '11, thus increasing theefliciency. The baffies formerly used in prior art devices between anodeand cathode increase the length of the arc discharge path and henceincrease the voltage drop therein, ipcrgase the wattage losses, decreasethe efiiciency', and aggravate the cooling problems. By the presentconstruction of a wetted film cathode, the natural configuration of atubeor' tank discharge devicemay' be utilized to best advantage. Thisalso permits operation of the tube in my attitude or position, evenchanging positions as in a moving vehicle, and it. is not required totake into account the action of gravity on any of the parts for properoperation as was true'in the prior art mercury pool type of dischargedevice. With the device 11 mounted with the axis 20 vertically, theentire cathode surface 17 is vertical as is the active'surface of theanode 13. If the "device 11 were operatedon its side, the active surfaceof the cathode'17 would'have two portions, one of which was'horizontaland'one of which was vertical. These would be two surface portions whichare mutually perpendicular, yet the device 11 would function normallywith a big advantage over the prior art mercury pool types which'couldbe operated'in only one position.

The Figure 2 shows a modified form of the invention to illustrate thatthe invention may be utilized in different forms of discharge devices.Figure 2 shows a discharge device 50 which is principally or at leastpartially of glass construction as opposed to the metal construction ofFigure 1. The anode 13 is'again supported on an anode shaft 21 in thiscase mounted and carried in the glass end cap 51. A metal shell 52 issealed in and forms a partof the envelope formed by the glass end cap 51and another glass end cap 53. The metal shell 52 is treated on theinside to be wetted with a mercury film to form the cathode 17; andhence, the metal shell 52 may be conveniently made of a refractorymetal'wettable with mercury such as molybdenum or tungsten. An anodeshield 54 is closely spaced to the anode shaft 21 and upper endoftheanode 13, and is either electrically floating or tied to thecathode through a resistor. This shield 54 establishes that the cathode17 is not exposed to the field of the anode 13 except through thestructure of the grid 55. This grid may be identical to the grid 14 ofFigure 1 but has been shown in a slightly different configuration.

A keep-alive anode 56 has been shown as an annular or cylindricalperforated metal or graphite shield surrounding the grid 55 andgenerally coextensive therewith. The keep-alive anode 56 is supported bymount and lead-in terminals 57. A starting electrode 58, a portion ofwhich is magnetic, is mounted on a pivot 59 and may be operated by anexternal electromagnet 60 to move the electrode 58 away from the cathode17 for initiating an electric discharge. Air cooling fins 61 areattached directlyto the outside of the cylindrical shell 52 radially forellicient heat transfer to the ambient atmosphere. The operation of thedischarge device 50 is essentially the same as that of the device ofFigure 1, the keep-alive anode 56 permitting discharge at any pointbetween the cathode 17 and keep-alive anode '56 which is most favorable.

The Figures 3-7 show a multi-electrode mercury vapor discharge device70. This device 70 is contained within a metal tank 71 supported onelectrical insulators 72. Figure 3 is a horizontal section through thistank 71 showing a plurality of hollow rectangular cathodes 73 and anodes74. Grids 75 are electrically and physically connected to the tank 71and surround the anodes 74.

Figure shows a vertical section through one of the cathodes 73 which isof hollow rectangular construction containing baffles 76 and supportedby two hollow terminals 77 and 78. These terminals are supported inmetal sleeves 79 and glass seals 80 to the tank 71 and a terminalconnecting portion 81 may be fastened to the hollow terminals 78 or 77.A coolant liquid may be circulated through the hollow terminal 78 anddirected by the'baffles 76 for efficient cooling of the cathode73 andexit through the hollow terminal 77. A starting electrode 82 movablewith respect to the cathode 73 may be provided as well as a keep-aliveanode 83.

Figure 6 shows a vertical section through one of the anodes 74 again ofhollow construction containing baflies 76 for directing of coolant fromone hollow terminal 84,

anything; suitable such as molybdenum or tungsten fastened to a basemetal 88. Another surface 89 is a nonwetted surface prepared by anysuitable means such as oxidation or covering with-colloidal graphiteemulsion. The thickness of the mercury film on the wettable surfaceis-not shown separately but may bein the nature of a few molecules inthickness.

The several anodes-74* maybe connected in parallel externally of thetank 71 as well as the several cathodes '73. This paralleling permitshigh current operation of the entire device which limits the amperagerequired'to be carried by each'particular anode. The grid beingelectrically connected to the tank 71 shields each of the anodes 74-from the cathodes on eitherside thereof and the insulators 72 for thetank 71 permit maintenance of thegrid potential at otherthan groundpotential.

The lower surface ofthe cathode 71 is preferably activated or atleast'permitted to be wetted by a mercury film as are the otherrefractory metal surfaces, and thus the construction of Figures 3-7showsa mercury discharge device which has three mutually perpendicularcahode surfaces which are active and which may support an electricdischarge between the. cathode 73 and the anode 74. This is trueregardless of the attitude of the tank 71.

The invention shows several constructions of mercury vapor dischargedevices which permit close spacing of the anode and cathode with aminimum of bathing therebetween for" minimum voltage drop and hencehigher eficiency. The'structure of Figures 3-7 is preferably operated sothat the heat exchanger connected to the liquid coolant of the cathodeis more efficient or at least maintains'thecathodes 73 at a lowertemperature than that of the anodes 74. This assures that the -mercuryfilm on the cathodes 73 will be maintained and that mercury will notcondense on the anodes 74. The rectangular construction'of Figures 3-7permits a maximum utilization of space within the tank 71 fora'multi-electrode structure and permits large active areas of both anodeand cathode with these surfaces beingsubstantially parallel andcoextensive.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to Withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. A mercury vapor discharge device comprising, an

anode, a cathode cooperating with said anode, insulating means mutuallyinsulating said anode and cathode, substantially perpendicular mercuryfilm wettable surface portions on said cathode disposed substantiallyparallel to and coextensive'with surface portions of said anode, and aperforate grid substantially coextensive with said wettable surfaceportions on said cathode.

2. In a mercury vapor discharge device, an anode, a cathode cooperatingwith said anode, substantially perpendicular mercury fihn wettablesurface portions on said cathode forming a discharge area disposedsubstantially parallel to and opposite corresponding surface portions ofsaid anode.

3. A mercury vapor discharge device comprising, a sealed envelope, ananode, a cathode, and a grid supported in said envelope in mutuallyinsulated relationship with said grid shielding said anode from thecathode, a substantially verticalsurface on each said anode and cathodedisposed substantially coextensive and parallel, means establishing saidvertical surface of said cathode as wetted by mercury, said mercurywetted surface establishing a mercury vapor atmosphere within saidenvelope, heat exchange means connected to one of said anode and saidcathode to maintain a mercury vapor pressure equilibrium to favormaintenance of a mercury film on said cathode wetted surface wherebysaid wetted vertical surface of said cathode is that from which thespace discharge to the anode takes place, and said grid having aperforate surface substantially coextensive and parallel with said anodeand with said cathode wetted surface.

4. A mercury vapor discharge device comprising, a sealed envelope atleast partially of metal and having an upper wall, an anode electricallyinsulated from said envelope and supported from said upper wall, acathode supported within said envelope, a grid shielding said anode fromthe cathode, insulator means mutually insulating said grid, anode andcathode, said anode and cathode being relatively closely spaced withonly the grid therebetween, heat exchange means connected to one of saidanode and said cathode to maintain said cathode cooler than said anodeduring operating conditions, first and second surface portionssubstantially mutually perpendicular on said cathode, first and secondsurface portions on said anode disposed substantially coextensive withand parallel to said first and second surface portions of said cathode,a keep-alive anode within said envelope disposed adjacent said cathode,a starting electrode disposed within said envelope for cooperation withsaid cathode, means forming a mercury film on said first and secondsurface portions of said cathode, said mercury film establishing amercury vapor atmosphere within said envelope portions, and said gridhaving a perforate surface substantially coextensive and parallel withsaid anode and with said cathode wetted surface.

5. A mercury vapor discharge device, comprising, an evacuated envelopehaving an axis, an anode disposed centrally on said axis, an annulargrid substantially axially coextensive with and surrounding said anode,an annular cathode substantially axially coextensive with said anode andforming a part of said envelope to surround said grid, and an activesurface on the interior of the axially coextensive part of said cathodeto establish an area for mercury vapor discharge beween said cathode andsaid anode through said annular axially coextensive grid, said cathodeas part of said envelope operating at a temperature to establish amercury vapor pressure in the envelope favoring maintenance of a mercuryfilm on said cathode.

6. A mercury vapor discharge device, comprising, a generally cylindricalevacuated envelope having an axis, a cylindrical anode disposedcentrally on said axis, means supporting and establishing electricalconnection to said anode, a cylindrical shell cathode substantiallyaxially coextensive with said anode and forming a part of said envelope,said anode being relatively closely spaced to said cathode withoutbaffles therebetween, means form ing a wetted mercury surface on theinterior of said cathode to establish an area for mercury vapordischarge between said cathode and anode, and a cylindrical perforatedgrid substantially axially coextensive with and surrounding said anode,and substantially axially coextensive wtih said wetted cathode surfacesaid cathode as part of said envelope having good heat transferrelationship with the ambient atmosphere, whereby said cathode operatesat a temperature not higher than that of said anode.

7. A mercury vapor discharge device, comprising, a generally cylindricalevacuated envelope having an axis and first and second ends, acylindrical main anode disposed centrally on said axis, a cylindricalperforated grid substantially axially coextensive with and surroundingsaid anode, first support and terminal means axially extending into saidenvelope from said first end to support said anode and provideelectrical connection thereto, second support and terminal means axiallyextending into said envelope from the second end thereof to support saidgrid and provide electrical connection thereto, a cylindrical shellcathode substantially axially coextensive with said anode andsurrounding said grid and forming a part of said envelope, a keep-aliveanode within said envelope and cooperating with said cathode, a movablestarting electrode within said envelope and cooperating with saidcathode, said main anode being relatively closely spaced to said cathodeWithout baffles therebetween, a mercury film on a substantial part ofthe interior portion of said cathode which is parallel to said anode toestablish an area for mercury vapor discharge between said cathode andmain anode, a mercury vapor atmosphere in said envelope established bysaid mercury film, and a mercury film non-wettable surface on portionsof said cathode and of said envelope which are other than parallel tosurfaces of said anode, said perforated grid being substantially axiallyparallel and coextensive with said mercury film cathode surface, saiddischarge area of the cathode being formed of a dense member ofarc-resisting metal and as part of said envelope having an envelopeexternal surface for good heat transfer relationship with the ambientatmosphere, whereby said cathode operates at a lower temperature thansaid main anode.

8. A mercury vapor discharge device, comprising, a generally cylindricalevacuated metal envelope having an axis and first and second ends, acylindrical main anode disposed centrally on said axis, a cylindricalperforated grid substantially axially coextensive with and surroundingsaid anode, first support and terminal means axially extending into saidenvelope from said first end to support said anode and provideelectrical connection thereto, second support and terminal means axiallyextending into said envelope from the second end thereof to support saidgrid and provide electrical connection thereto, a cathode formed fromthat portion of said metal envelope which is substantially axiallycoextensive with said anode, a keep-alive anode within said envelope andcooperating with said cathode, a movable starting electrode cooperatingwith said cathode, said main anode being relatively closely spaced tosaid cathode without baffies therebetween, means forming a wettedmercury surface on the interior of the axially coextensive part of saidcathode to establish an area for mercury vapor discharge between saidcathode and main anode, means including said wetted mercury surfaceestablishing a mercury vapor atmosphere in said envelope, and liquidcooling conduits connected directly to the outer surface of saidenvelope at said cathode portion thereof, whereby said cathode operatesat a lower temperature than said main anode.

9. A mercury vapor discharge device, comprising, a generally cylindricalevacuated partially glass envelope having an axis and first and secondends, a cylindrical main anode disposed centrally on said axis, acylindrical perforated grid substantially axially coextensive with andsurrounding said anode, first support and terminal means axiallyextending into said envelope from said first end to support said anodeand provide electrical connection thereto, second support and terminalmeans axially extending into said envelope from the second end thereofto support said grid and provide electrical connection thereto, acylindrical shell cathode substantially axially coextensive with saidanode and sealed in as part of said envelope with said cathode having anexposed exterior metal surface, a cylindrical perforated keep-aliveanode substantially axially coextensive with and surrounding said gridand disposed adjacent said cathode, a movable starting electrodecooperating with said cathode, said main anode being relatively closelyspaced to said cathode without baflles therebetween, means forming awetted mercury surface on the interior of the axially coextensive partof said cathode to establish an area for mercury vapor discharge betweensaid cathode and main anode, means including said wetted mercury surfaceestablishing a mercury vapor atmosphere in said envelope, and aircooling fins directly connected to said exposed exterior metal surfaceof said cathode, whereby said cathode operates at a lower temperaturethan said main anode.

10. A mercury vapor discharge device comprising, a rectangular metaltank having upper and bottom walls, a hollow anode and a hollow cathodewithin said tank, first and second hollow electrical terminalsinsulatedly carried in said upper wall supporting said anodeelectrically insulated from said tank, third and fourth hollowelectrical terminals insulatedly carried in said upper wall supportingsaid cathode electrically insulated from said tank, a grid electricallyconnected to said tank and surrounding said anode to shield said anodefrom the cathode, insulator means insulating said tank and grid fromground, liquid coolant inlet and outlet means through the two terminalsof each said anode and cathode, means to circulate liquid coolantthrough said anode and said cathode to maintain said cathode cooler thansaid anode during operating conditions, first and second substantiallyvertical surfaces on each said anode and cathode disposed substantiallycoextensive and parallel, said cathode having a lower surface adjacentthe bottom of said tank, a keep-alive anode within said tank disposedadjacent said cathode, a starting electrode disposed within said tankfor cooperation with said cathode, means forming a mercury film at leaston portions of said first and second vertical and lower surfaces of saidcathode, and means including said mercury film establishing a mercuryvapor atmosphere within said tank.

11 A multi-electrode mercury vapor discharge device comprising, arectangular metal tank having upper and bottom walls, a plurality ofhollow anodes and cathodes within said tank, first and second hollowelectrical terrninals insulatedly carried in said upper wall supportingeach said anode electrically insulated from said tank, third and fourthhollow electrical terminals insulatedly carried in said upper wallsupporting each said cathode electrically insulated from said tank, saidanodes and cathodes being alternately spaced in said tank, a series ofgrids electrically connected to said tank and surrounding each of saidanodes to shield each anode from the cathodes on either side thereof,insulator means insulating said tank and grids from ground, baffleswithin each said anode and cathode to provide a lengthened coolant path,liquid coolant inlet and outlet means through the two terminals of eachsaid anode and cathode, means to circulate liquid coolant through saidanodes and said cathodes to maintain said cathodes cooler than saidanodes during operating coditions, first and second substantiallyvertical surfaces on each said anode and cath ode disposedsubstantiallycoextensive and parallel, each of said cathodes having alower surface adjacent the bottom of said tank, a keep-alive anodewithin said tank disposed adjacent at least one of said cathodes, astarting electrode disposed within said tank for cooperation with atleast one of said cathodes, means forming a mercury film on said firstand second vertical and lower surfaces of each said cathode, andmeansincluding said mercury film establishing a mercury vapor atmospherewithin said tank.

12. A mercury vapor discharge device, comprising, an evacuated envelopehaving an axis, an anode disposed centrally on said axis, an annularperforated grid substantially axially coextensive with and surroundingsaid anode, means supporting and establishing electrical connection tosaid anode and said grid, an annular cathode substantially axiallycoextensive with said anode and forming a part of said envelope, acoaxial portion of said cathode having a mercury wettable refractorymetal active surface to establish an area for mercury vapor dischargebetween said cathode and anode through said grid, said cathode as partof said envelope having good heat transfer relationship with theambient, whereby said cathode operates at a temperature not sufiicientlyhigher than that of said anode to prevent maintenance of a mercury filmon said cathode.

References Cited in the file of this patent UNITED STATES PATENTS

